Schistosomiasis (bilharziasis) is a parasitic disease caused by schistosomes (blood flukes) that generally live in the veins of the gut and liver of a human host. Adult worms can survive up to 20 years, and heavy infestations block blood vessels. The mere presence of even a few adults acts as a focus of inflammation and infection. Worse, female adult worms release thousands of eggs each day, which often find their way to tissues such as liver, brain, and lung, where they cause considerable damage by stimulating the body to form cysts and scar tissue around them.
Most eggs, however, pass through the bladder or wall of the gut. Once outside, they hatch and infect water snails. The parasite multiplies inside the snail, giving rise to thousands of cercariae that exit the snail and swim free in search of a host in which to complete their life cycle. When the cercaria makes contact with skin, it releases a serine protease that dissolves the protein of the skin, affording entry into the body.
The World Health Organization estimates that over 200 million people worldwide suffer from schistosomiasis. Treatments are available, but because the disease is so debilatiting, preventing the disease is preferable to treating it. This is especially true in the case of soldiers and engineers deployed in the tropics who must sometimes work in and around infested waters.
The United States Army has identified a compound that prevents infection by the schistosomiasis parasite. This compound, niclosamide, which was originally developed to kill snails, can be added to lotions, creams and sprays for topical administration, or can be incorporated into soap. See generally, Cherfas, J. 1989. Science 246, 1242-1243.
Despite the availability of niclosamide, there is a need for other anti-penetrant compounds that can inhibit invasion of skin by schistosome larvae. Accordingly, it is an object of the present invention to provide anti-penetrant compounds that can inhibit invasion of skin by schistosome larvae. Another object of the invention is to provide synthetic compounds that inhibit the enzyme(s) used by the schistosome larvae to invade skin. It is a further object of the present invention to provide compositions that contain synthetic compounds that inhibit serine protease(s). Such compositions can be applied topically via lotions, creams, sprays or soaps, etc., to inhibit or prevent cercariae from penetrating the skin.